In 2006, Sony tested the patience of e-book fans by twice delaying the release of its PRS-500 reading device, originally set for the spring. The company finally started taking orders over the Web in September, and the gadget can now be bought at electronics stores and some Borders bookstores.

It was worth the wait. The Sony Reader’s selling point is its black-and-white “electronic paper” screen, which has been advertised as a far better imitation of ink on paper than the LCDs found in laptops, cell phones, and earlier generations of e-book reading devices. After curling up for a couple of weeks with a unit lent to me by Sony, I’m happy to report that it lives up to its billing. It isn’t a replacement for paper–but it is the first e-book device that works well enough to appeal to a large swath of readers, even given its $350 price tag.

If electronic publishing is to take off, a good reading device will be necessary but not sufficient. Sony’s system for delivering e-books has a key weakness: content is too expensive. At the prices Sony and its publishing partners are charging for the e-book versions of current hardcovers, just 25 books will set you back about $350. The same problem has derailed almost every attempt at making electronic books into a mass-market product.

I’d been waiting for Sony to release an English-language e-book reader since 2004, when it introduced its first e-paper device, the Librié, in Japan. My interest in electronic-paper technology dates back to 1999-2001, when I served as managing editor for a technology news site called eBookNet. The site was owned by a startup called NuvoMedia, which manufactured the Rocket eBook, an elegant little device that captured my fancy when I first reviewed it–for Technology Review–in 1999. NuvoMedia is now defunct, the victim of high e-book prices imposed by publishers and an ill-conceived merger with Gemstar-TV Guide International. Most of its competitors went down, too. Sony was one of the first to reënter the market.

Even in my NuvoMedia days, I was aware of the technology being developed by E Ink, a startup in Cambridge, MA, founded in 1997 by researchers at MIT’s Media Lab (see “Electronic Paper Turns the Page,” March 2001). Their clever idea: sandwich millions of tiny, liquid-filled microcapsules between two layers of electrodes, the top one transparent. Floating inside each microcapsule are thousands of positively charged white particles and negatively charged black particles. A negative charge applied at a given electrode on the lower layer pulls the white particles to the bottom of nearby microcapsules and pushes the black particles to the top, creating a black mark beneath the transparent electrode; clusters of these marks make up the equivalent of a black pixel in an LCD screen. This held out the promise of both higher resolution (since the pixels can be made smaller than those in LCDs) and longer battery life (since the particles stay in place, without any further electricity use, until the user calls up the next page). And this is the technology that Sony licensed for the Librié and the Reader PRS-500.

I’d long wanted to see E Ink’s technology in action. And as it turns out, the Reader’s six-inch-diagonal display is a beauty. It’s 800 pixels high and 600 pixels wide, giving it a resolution of roughly 170 pixels per inch (that trounces a standard LCD’s 90 to 120 pixels per inch), which means characters appear sharper and smoother than on other displays. The Reader’s screen doesn’t achieve the crispness of black text on the thick, bleached pages of a hardcover book. But the contrast ratio of the Reader’s screen–the brightness of the whites measured against the deepness of the blacks–is 8:1, which puts it on a par with newsprint.